be weary of the ADHD tests on such a young child. Or at least mindful of the shortcomings. As you know, the tests are scored on a bell curve for 'normal' development at a given age. The more data points, the more accurate the test results, and the more useful the outcomes. What I discovered when we had our son tested at 6 (or maybe 7), is that there is very little data for that age category. So there was a lot of "well, he tests low here... and that could be down to many different factors, we can't be sure what the cause is and how to address the issue"... I discovered that it isn't till grade 3 that you get enough data points to really be able to make use of the diagnosis.
On the other hand, having the diagnosis is a tool you can take to the school/teachers and explain your kids' needs, and not have them mislabeled with unhelpful labels (such as "problem child" for example)...
either way... good luck.